Deep-Sea Volcanoes: Biological Hotspots Are Windows Into the Subsurface

Magmatic gas hydrothermal venting at the Cone site in Brothers volcano.
Credit: Image courtesy of Anna-Louise Reysenbach, NSF, ROV Jason and 2018©Woods Hole Oceanographic Institution.

Hydrothermally-active submarine volcanoes account for much of Earth’s volcanism and are mineral-rich biological hotspots, yet very little is known about the dynamics of microbial diversity in these systems. Recently in Proceedings of the National Academy of Sciences (PNAS), Reysenbach and colleagues, show that at one such volcano, Brothers submarine arc volcano, NE of New Zealand, the geological history and subsurface hydrothermal fluid paths testify to the complexity of microbial composition on the seafloor, and also provide insights into how past and present subsurface processes could be imprinted in the microbial diversity.

“Microbes in hot springs everywhere get their energy in part from the geochemistry of the hot water/fluids. It’s the same for the Brothers volcano seafloor hot springs. Since both seawater- and magmatic gas-influenced hydrothermal systems coexist at Brothers, we predicted that the microbes in the active magmatic cone sites (image on top of page) would be very different from those on the caldera wall (image below) that are affected largely by modified seawater,” said Reysenbach, Professor of Microbiology at Portland State University. But what they did not expect was that there would also be two very different microbial communities in close proximity to each other on the caldera wall.

From recent International Ocean Discovery Program (IODP) drilling and geophysical measurements there is evidence that after the volcanic caldera collapse of the original stratovolcano to form the present-day caldera, the earliest magmatic-hydrothermal system became overprinted by a more seawater dominated system. The authors show that one of the caldera communities aligns with microbes from magmatically-influenced hydrothermal vents of the more recent cone that has grown up from the caldera floor. It is likely that a combination of different subsurface mineral assemblages intersected by the circulating hydrothermal fluids helps shape distinct microbial communities on the caldera wall.

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